<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<span th:if="${age>=19}">真好</span><br/>
<span th:unless="${age>=19}">真不好</span><br/>
</body>
</html>